The invention concerns a process for producing sintered parts from an aluminum sintering mixture.
A wear-resistant sintered aluminum alloy which comprises in parts by weight between 2.4 and 23.5% of Si, between 2 and 5% of Cu, between 0.2 and 1.5% of Mg, between 0.01 and 1% of one or more elements from the group consisting of the transition metals Ti, V, Zr, Mn, Fe, Co, Ni and Nb, and the balance aluminum, with inevitable impurities, is known from EP 0 669 404 B1. The alloy has a fleck-like grain structure comprising an Al-mixed crystal phase and an Al-Si-alloy phase, wherein the latter has dispersed hypereutectic Si-crystallites with a maximum diameter of between 5 and 60 xcexcm and the region of the Al-mixed crystal phase is between 20 and 80% of the cross-section of the fleck grain structure. In addition, a process for producing a wear-resistant sintered aluminum alloy is known from the above-indicated document, comprising the process steps:
producing a mixture of between 20 and 80% by weight of Al-Si-alloy powder with between 13 and 30% by weight of Si and between 80 and 20% by weight of Al-powder,
adding a Cu-transition metal alloy powder with between 0.2 and 30% by weight of one or more of the transition metals Ti, V, Cr, Mn, Fe, Co, Ni, Zr and Nb, and an Mg-powder or an Alxe2x80x94Mg-alloy powder with 35% by weight or more of Mg to form the mixture of Al-powder and Alxe2x80x94Si-alloy powder, thereby affording a powder mixture of a composition comprising between 2.4 and 23.5% by weight of Si, between 2 and 5% by weight of Cu, between 0.2 and 1.5% by weight of Mg and between 0.01 and 1% by weight of the transition metal, with the balance being aluminum and with inevitable impurities, compacting of the powder mix obtained in that way to form a green sintered preform, and terminating with sintering of the green sintered preform to afford the sintered part.
In that case, the hypereutectic Si-crystallites which are contained in the Alxe2x80x94Si-alloy phase in the. sintered aluminum alloy grow to a size of between 5 and 60 xcexcm. In that procedure, heating of the entire body or only the outside surface of the sintered aluminum alloy is effected. The heating procedure is followed by cooling. That known process for producing a wear-resistant sintered aluminum alloy is based on taking a binary Al-Si-alloy powder as the starting material, to which are added Al-powder and the alloying powder in the form of Mg-powder or Al-Mg-powder and Cu-powder or Cu-alloy powder. Due to those added alloy powders, low-melting phases are formed, by which liquid phase sintering is possible.
EP 0 436 952 B1 discloses a mixed aluminum alloy powder for the production of a compacted and sintered aluminum alloy, comprising a mixture of the following components:
an aluminum alloy primary initial powder (A) which (in terms of weight) comprises the following constituents:
between 0.1 and 3.0% of Cu and
optionally between 0.1 and 2.0% of at least one element selected from Mn, Ni, Fe, Cr, Zr, Ti, V, Pb, Bi and Sn, wherein the balance is Al and inevitable impurities, and
a master alloy initial powder (B) comprising the following constituents (in percent by weight):
between 4 and 20% of Mg,
between 12 and 30% of Si and
optionally between 0.1 and 8% of at least one of the elements Mn, Ni, Fe, Cr, Zr, Ti, V, Pb, Bi and Sn, with the balance being Al and random impurities. The master alloy powder (B) can also comprise the following constituents (in percent by weight):
between 4 and 20% of Mg,
between 12 and 30% of Si,
between 1 and 30% of Cu, and
optionally between 0.1 and 8% of at least one of the elements Mn, Ni, Fe, Cr, Zr, Ti, V, Pb, Bi and Sn,
with the balance being Al and random impurities,
wherein the master alloy (B) is present in a range of between 2 and 15% in order to obtain the following composition in the mixed powder (in percent by weight):
between 0.1 and 2.0% of Mg,
between 0.1 and 2.0% of Si,
between 0.2 and 6% of Cu and
optionally 4.0% or less overall of Mn, Ni, Fe, Cr, Zr, Ti, V, Pb, Bi and/or Sn.
This involves an aluminum alloy powder for the production of aluminum sintered parts, wherein two aluminum alloy powders are mixed together. After that mixing operation the composition is as follows:
between 0.1 and 2% by weight of Si,
between 0.2 and 6.0% by weight of Cu,
between 0.1 and 2% by weight of Mg, and
optionally 4% by weight or less of Mn and/or Ni and/or Fe and/or Cr and/or Zr and/or Ti and/or V and/or Pb and/or Zr and/or Sn.
The composition of the alloy powders used in this case also makes it possible to form low-melting phases and thus liquid phase sintering.
The low-melting phases which occur in liquid phase sintering mean that, during the heating operation, growth and/or shrinkage phenomena occur and therefore the sintering process can only be controlled with difficulty. The liquid phase component during the sintering operation means that it is often not possible to prevent distortion of the sintered parts produced, thus resulting in unwanted dimensional variations. The mechanical properties of the sintered parts produced may fluctuate within a relatively wide range of values.
The object of the present invention is to provide a process of the kind set forth in the opening part of this specification with which it is possible to produce sintered parts with excellent resistance to wear and a high level of mechanical strength, while the sintering procedure can be implemented in a relatively easily controlled fashion and distortion of the sintered parts produced can be avoided.